Production of solid fuel agglomerates



Filed Aug. 15, 1946 OmJ m m a g Jm301 Q4 All. mm mm a BN wv dmEzoad m3 1 04 4N y 9 m A,

IV UN k jr z j. g g og ZSrIVeabor's Clbborrzegs Patented July 10, 1951 rnonuc'rron F soLm FUEL AGGLOMERATES Homer Z. Martin, Roselle, and Karl J.

Nelson,

Cranford, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application August 15, 1946, Serial No. 690,817

1 The present invention relates to the production of solid fuel agglomerates from carbonizable fuels and more specifically to an improved method of producing highly reactivesmokeless coke agglomerates, preferably in the form of lumps or spheroidal briquettes from carbonizable fuels such as coal, lignite, brown coal, asphalt, petroleum, cellulosic material including lignin, etc.

3 Claims. on. 202-6) leaves a very hard carbonaceous scale on the walls, particularly of the plastic zone, of the kiln. This scale is difficult to remove and seriously interferes with a continuous operation of the Moreover, the process which for economic operation requires a strongly coking plasticizing coal charge is bound to low carbonization tempera- For the purpose of producing a smokeless fuel it is necessary to drive ofi most or all of the normally liquid hydrocarbons such as tar oils which means that carbonizable fuels may be rendered smokeless by a carbonizing treatment at temperatures up to about 1000 F. or higher. However, the flnely divided coke normally obtained in the course of conventional carbonization treatments has a very low content of agglutinating constituents and may not readily be converted into stable agglomerates of useful briquette size and strength.

It has, therefore, been suggested prior to the present invention, to combine the carbonizing treatment with the briquetting step in a process utilizing the property of certain strongly coking coals to pass through a plastic state and to develop agglutinating tendencies within a definite range of elevated temperatures. In this process, fines of strongly coking coals having a particle size of minus in. and less are passed through an inclined rotary kiln heated externally by a countercurrently flowing heating gas to a final temperature of about 850-900 F., which is slightly above the minimum carbonization temperature of the coal charge. The coal, while undergoing carbonization, passes through the plastic state at about 600-800 F. The rotating motion of the kiln causes the plastic agglutinating particles to agglomerate to form spheroids or balls of low temperature coke, having diameters of about l-6 in. Coal gas, light oil, tar and an acidic liquor are recovered as volatile carbonization products.

The low temperature coke obtained ,by this process has the desirable characteristics of high reactivity, smokelessness, high mechanical strength, and convenient size. However, the economics of the process suffer considerably from relatively poor yields of volatile carbonization products. Particularly the tar yields are materially lower than in conventional low temperature carbonization and usually fail to exceed 8% by weight or about 14-16 gals. per ton of coal charged as compared with about -12% or 20-25 gals. for conventional operation if a coal containing about 30-35% of volatile matter is used. In addition, the coal becoming plastic within the retort tures and is relatively inflexible with respect to amount and composition of volatile carbonization products.

Strongly coking coal must be "thermodized by a mildly oxidizing treatment in order properly to modify the agglutinating character of the fresh coal. This treatment requires expensive additional equipment without compensation in the form of product yield and in most cases leads to lower tar yields and qualities.

In addition the use of strongly coking coals necessitates a recirculation of coke fines obtained from the process to establish the proper ratio of dry and agglutinating materials, required for ball formation. The so-called coke breeze, that is the coke fines formed in the rotary kiln and from subsequent cooling and conveying, in addition to the product coke balls, is insuflicient for this purpose so that a substantial portion of marketable product coke must be crushed to provide the amount of breeze required for recirculation.

The indirect heat supply through the kiln walls in combination with the larger size of the coal aggregates to be heated to carbonization temperature leads to excessive temperature requirements in the heating jacket and seriously limits the carbonization temperature. In addition there exists always a considerable temperature gradient across the radius of the individual coal balls resulting in irregular carbonization of these coal balls. In actual operation, it has been found that the temperatures permissible for practical construction materials are insufficient to heat the kiln charge indirectly to the desired carbonization temperatures. It has therefore been necessary to admit an oxidizing gas such as air into the discharge and of the kiln so as to generate additional heat by a partial combustion of solid and/or volatile carbonization products, resulting in additional losses.

The present invention overcomes the aforementioned difliculties and aflords various additional advantages. These advantages, the nature of the invention and the manner in which it is carried out will be fully understood from the following description thereof, read with reference to the accompanying drawing.

-It is, therefore, the main object of our invention to provide an improved method of producing highly reactive, smokeless coke agglomerates from carbonaceous materials.

Another object of our invention is to improve the tar yield in the manufacture of highly reactive spheroidal smokeless coke briquettes from carbonaceous materials.

A further object of our invention is to make the manufacture of highly reactive smokeless coke briquettes from carbonaceous materials independent of the use of specific coals and low carbonization temperatures.

A still further object of our invention is to make more flexible the manufacture of highly reactive smokeless spheroidal coke briquettes from coal fines with respect to amount and composition of volatile carbonization products.

Other objects and advantages of our invention will appear hereinafter.

We have found that these objects may be accomplished, quite generally, by subjecting finely divided carbonizable fuels to carbonizing conditions in the form of a dense turbulent mass of solids fluidized by an upwardly flowing gas to form a well defined upper level and converting the finely divided coke formed into agglomerates of the desired size and mechanical strength with the aid of a suitable hydrocarbon binder such as crude petroleum, petroleum residue, coal pitch, heavy ends of the coal tar formed in the carbonizing step, etc. The amount of binder depends on the specific briquetting method applied and to some extent on the character of the coke produced in the carbonization step. In general, relatively small proportions of binder varying between about 3 to 15% by weight of coke are su fficient for the purpose of our invention. The final product is a smokeless coke briquette whose reactivity is materially higher than that of the coke itself as a result of the presence of the more highly reactive binding materials.

In accordance with the preferred embodiment of our invention the flnely divided coke recovered from the fluid carbonization stage and a small amount of carbonaceous binder are passed together through a rotary kiln at elevated temperatures of about 600-900 F. On its way through the rotary kiln, the coke is uniformly impregnated with the binder so as to become agglutinating. As a result of the rotary motion of the kiln, the agglutinating coke agglomerates to form spheroidal or ball-shaped coke briquettes of high mechanical strength varying in size from about 1 to about 8 in. diameter.

It will be appreciated from the foregoing general description that our invention permits the manufacture of smokeless highly reactive coke briquettes from any desired carbonizable fuel. The process may be operated at carbonization conditions optimum for any type of starting material without affecting the formation of the coke briquettes. Carbonization of the finely divided starting material in the form of a dense turbulent mass of fluidized solids permits a perfect control of carbonization conditions including ideal heat distribution and uniformity of temperature resulting in optimum yields of desired volatile carbonization products. Particularly in combination with low temperature carbonization, our process aifords the recovery of coal tar yields as high as about 30% by weight of the coal charged. Moreover, the coal is deprived of its plasticizing tendency prior to its entry into the rotary briquetting kiln whereby deposits of carbonaceous scale are materially reduced.

The separation of carbonization from briquetting in acordance with our invention makes a Thermodizing" treatment superfluous. The asglutinating property of the charge to the briquetting kiln may be controlled by the amount of binder added and no product need be crushed and recirculated in order to establish the desired ratio between dry and agglutinating constituents. The briquetting process is entirely independent with respect to the heat requirement for the carbonization with the result that both indirect and internal heating of the briquetting kiln may be omitted, if desired, the sensible heat of the coke fines supplied from the fluid carbonizer and of the preheated binder being sufficient for the briquetting operation. It is also noted that the particle size required for proper fiuidization is about the same as that required for the formation of spheroidal briquettes so that no intermediate sizing of the charge is required.

Having set forth the general nature and objects, our invention will be best understood from the more detailed description hereinafter in which reference will be made to the accompanying drawing which shows a semi-diagrammatic view of apparatus suitable for carrying out a preferred embodiment of our invention.

Referring now in detail to the drawing, the apparatus illustrated essentially comprises a carbonization reactor l0 and a rotary kiln 40 the functions and cooperation of which will be presently explained using the manufacture of smokeless coke briquettes from a carbonization coal as an example. However, it should be understood that other carbonaceous starting materials may be used.

Finely divided carbonization coal having a particle size of less than in., preferably mostly between 8 and 200 mesh is supplied from feed hopper i by a suitable conveying means such as a screw conveyor or a standpipe 3 provided with aeration taps 5 and slide valve 1 to carbonizer I. If desired the coal in hopper I may be preheated with gases from the process, supplied through line 2, to temperatures of about 200600 F. which lie below the carbonization, plastic and ignition temperatures of the coal. If no coal preheating is desired a fiuidizing gas such as steam, flue gas, air, etc. may be introduced through line 2 to facilitate the flow of the coal particles. A similar fluidizing gas is injected, in small amounts, through taps 5 into standpipe 3 to maintain the fluid character of the solids column therein.

The fluidized coal is forced under the pseudohydrostatic pressure of standpipe 3 at a rate controlled by slide valve 1 into carbonizer l0 wherein it forms above distribution grid I2 a. dense turbulent mass of solids fluidized by the volatile carbonization products and a gas injected by blower I5 through line l1 below grid 12. Superficial gas velocities of about 0.3-3 ft. per sec. within carbonizer in are generally suitable for this purpose. The carbonization temperature in carbonizer l0 may be selected exclusively with a view to the type and quantity of volatile carbonization products desired and. may vary within the wide limits of about 800-2000 F. The lower temperatures within that range are inducive to the formation of relatively large quantities of low temperature tar and light oils while at the higher temperatures more coal gas and nitrogenous products are formed.

The heat required to maintain the desired carbonization temperature may be supplied in any conventional manner, for instance indirectly, or

as sensible heat of the gas introduced through line H or by an exothermic reaction within carbonizer l0, such as a limited combustion of coal constituents or by the circulation of externally heated char. superheated steam, hot flue gases or the like are preferred heating gases in the case of low temperature carbonization. When the carbonization is conducted at temperatures above about 1000 F., we may use air and/r oxygen preheated to about 600-800 F. in amounts sufficient to generate, by combustion, the heat required for carbonization. About 0.3 to 1.0 lb. of air per lb. of coal is normally adequate for this purpose, the exact proportion depending on the character of the coal, the degree of preheat and the temperature desired.

Volatile carbonization products are withdrawn overhead above level Lio, passed through a conventional gas-solids separator I9 provided with solids return line 2|, and removed from the system through line 23 for any further treatment or use desired. Separator l9 may also be arranged downstream of some conventional cooling means if the high temperatures of carbonizer l0 make this appear more advisable. I

Substantially "dry finely divided coke is withdrawn downwardly from earbonizer, l0 through line 25 aerated with a fluidizing gas through tap 21 and controlled by slide valve 29. The coke flows substantially at the temperature of carbonizer I0 into feeding device 3| of rotary kiln 40. Simultaneously, a liquid carbonaceous binder such as petroleum or coal pitch or heavy ends of coal tar which may be kept at, or preheated to, an elevated temperature of about 150 to 800 F., by means of heat exchanger 34 and which may be dissolved in a suitable solvent such as light oils to promote its flow, is added from tank 35 through line 33 to feed device 3|. The relative amount of binder added to the coke is carefully controlled so that it is sufficient for the desired briquetting efiect without impairing the smokeless character of the final coke briquettes. About 3 to 15% by weight of binder is generally suitable for this purpose.

The well heat-insulated kiln is preferably designed and operated so that it permits a briquetting time of the coke charge of about 5 to 100 minutes at temperatures varying from about 700-1000 F.

When the hot coke-binder mixture enters rotary kiln 40, any liquid binder not previously absorbed by the coke is evenly distributed over the inner kiln surface and picked up from there by the tumbling coke particles to cause substantially uniform impregnation of the coke with binder. The now agglutinating coke particles, on their downward path through the rotary kiln, agglomerate to form ball shaped briquettes of 1-8 in. diameter, allowedto bake to attain a high mechanical strength and to be free of smoking low-boiling binder constituents. The coke balls discharge through line 49 into receiver 50 wherein they may be cooled below ignition temperature in a manner known per se. Coke fines formed by abrasion and collected in receiver 50 may be returned to feed device 3| by any conventional means.

The process is preferably operated continuousveying means such as screw conveyors or the like.

Instead of feeding a. mixture of coke and binder to rotary kiln 40 these two materials may be charged separately to the kiln. The binder may 5 also be added in increments along the path of the coke in order to control the time within which the coke remains agglutinating. In this manner the size of the coke balls may be more readily controlled. Other modifications of the embodiment of our invention illustrated by the drawing will appear to those skilled in the art.

When a liquid carbonizable fuel is used as the starting material it may be injected into a fluidized bed of finely divided carbonaceous or non-carbonaceous solids such as coke, sand, or the like maintained at carbonization temperature in carbonizer l0.

Our invention will be further illustrated by the following specific example.

When combining fluid carbonization with the production of spheroidal coke briquettes in a rotary kiln, in accordance with the preferred embodiment of our invention the process may be operated at the conditions given below.

Fluid carbonization conditions Raw coal feed, lbs/hr 2000 Raw coal proximate analysis:

Volatile matter weight per cent 32.2 Moisture 5.6 Ash 9.4 Fixed carbon 52.8 Raw coal particle size, cumulative:

On 8 mesh weight per cent 0.2 On 14 mesh d0 22.2 On 48 mesh do 77.2 On 100 mesh do 88.8 On 200 mesh do 96.2 T 200 mesh do 3.8 Carbonization temperature, F 850 Air to carbonizenlbsjhr 700 Superficial fluidizing velocity, ft. per sec Briquetting conditions Fluid" coke feed pounds 1440 Petroleum pitch binder at 500 F do 70 Temperature in briquetter F 800 Briquetting time, min 10 Yields from process Briquettes (coke balls) pounds-.. 1500 Low temp. tar gal1ons.. 25

Reactivity of coke balls T15 and T15 are the temperatures at which the rate of heat release by oxidation of a sized sample becomes great enough to raise its temperature at rates of 15 C. per min. and 75 C. per minute respectively. (Sebastian and Mayer Ind. and Eng. Chem. 129, 1118 (1937).)

When the same amount of a similar coal is subjected in the conventional manner to simultaneous carbonization and coke ball formation in an externally heated rotary kiln the product yields are only 15 gals. of low temperature tar k and 1440 lbs. of coke balls having reactivities of T15=205 and T75=265. Our invention has been explained above with reference to the manufacture of coke balls in a rotary kiln and this embodiment of our invention is greatly superior to combinations with other 'briquetting procedures with respect to process economies'and productquality. However. it is noted that certain of the advantages of our invention may be realized when applying other briquetting procedures such as conventional pressure-briquetting to a mixture of carbonaceous binder with coke obtained from a fluid carbonization treatment in accordance with our invention. In this manner, a highl reactive lowsmoke coke briquette may be obtained together with optimum yields of volatile carbonization prdoucts.

While the foregoin description and exemplary operations have served to illustrate specific applications and results of the invention other modifications obvious to those skilled in the art are within the scope of the invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

we claim:

1. The process of producing a smokeless highly reactive solid fuel which comprises heating bituminous coal of fluidizable size in a vertical heating zone in the form of a dense turbulent bed of finely divided solids fluidized by an upwardly flowing gas containing free oxygen to resemble a boiling liquid having a defined upper interface within said zone, to a temperature of about 850 F., withdrawing finely divided highly heated carbonaceous solids from said bed, supplying said heated solids substantially at said temperature to a second heat-treating zone, supplying a minor proportion of liquid agglutinating carbonaceous substances selected from the group consisting of petroleum and coal pitch and heavy ends of coal tar to said second zone, subjecting the total charge of said second zone to a tumbling motion on a rotary supporting surface within said second zone at a temperature substantially lower than said first-named temperature, at conditions adapted and for a time sufllcient to effect the formation of spheroidal coke aggregates and substantial carbonization of said agglutinating substances, controlling the supply of said heated solids to said second zone in such a manner that at least a major portion of the heat required to maintain said second-named temperature is sensible heat of said supplied heated solids, and withdrawing carbonized carbonaceous solids from said second zone.

2. The process as claimed in claim 1 wherein said agglutinating substances are added in amounts varying from about 3 to 15% by weight of coke. I

3. The process of claim 1 wherein said agglutinating substances are added in increments to said solids while being subjected to said tumbling motion.

HOMER Z. MAR'I'IN. KARL J. NELSON.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 1,415,201 Smith May 9, 1922 1,495,573 Cantieny May 27, 1924 1,562,723 Pyzel Nov. 24, 1925 1,602,819 Jakowsky Oct. 12, 1926 1,618,563 Bascon Feb. 22, 1927 1,756,896 Wisner Apr. 29, 1930 1,772,189 McIntire Aug. 5, 1930 1,775,323 Runge Sept. 9, 1930 1,983,943 Odell Dec. 11, 1934 1,984,380 Odell Dec. 18, 1934 2,287,437 Fisher et a1 June 23, 1942 2,462,366 Davies Feb. 22, 1949 FOREIGN PATENTS Number Country Date 301,974 Great Britain Dec. 13, 1928 301,975 Great Britain Dec. 13, 1928 335,740 Great Britain Oct. 2, 1930 

1. THE PROCESS OF PRODUCING A SMOKELESS HIGHLY REACTIVE SOLID FUEL WHICH COMPRISES HEATING BITUMINOUS COAL OF FLUIDIZABLE SIZE IN A VERTICAL HEATING ZONE IN THE FORM OF A DENSE TURBULENT BED OF FINELY DIVIDED SOLIDS FLUIDIZED BY AN UPWARDLY FLOWING GAS CONTAINING FREE OXYGEN TO RESEMBLE A BOILING LIQUID HAVING A DEFINED UPPER INTERFACE WITHIN SAID ZONE, TO A TEMPERATURE OF ABOUT 850* F., WITHDRAWING FINELY DIVIDED HIGHLY HEATED CARBONACEOUS SOLIDS SUBSTANTIALLY AT SAID TEMPERATURE TO HEATED SOLIDS SUBSTANTIALLY AT SAID TEMPERATURE TO A SECOND HEAT-TREATING ZONE, SUPPLYING A MINOR PROPORTION OF LIQUID AGGLUTINATING CARBONACEOUS SUSBSTANCE SELECTED FROM THE GROUP CONSISTING OF PETROLEUM AND COAL PITCH AND HEAVY ENDS OF COAL TAR TO SAID SECOND ZONE, SUBJECTING THE TOTAL CHARGE OF SAID SECOND ZONE TO A TUMBLING MOTION ON A ROTARY SUPPORTING SURFACE WITHIN SAID SECOND ZONE AT A TEMPERATURE SUBSTANTIALLY LOWER THAN SAID FIRST-NAMED TEMPERATURE, AT CONDITIONS ADAPTED AND FOR A TIME SUFFICIENT TO EFFECT THE 